1. Field of the Invention
The invention relates to a laser diode module with an adjustable monitoring current, and more particularly to a photo diode arranged in array.
2. Description of the Related Art
Generally, a laser diode is provided with a photo diode. As shown in FIGS. 1 and 2, the photo diode is employed to receive the light emitted from the rear end of the laser diode, thereby creating a monitoring current. Theoretically, the light-emitting ratio of the front and read ends of the laser diode is a fixed value. Therefore, the monitoring current created by the photo diode can be used for the automatic power control circuit 10 to monitor the light-emitting power of the laser diode. When the power of the laser diode drops due to the rise of the ambient temperature, the power of the light shining on the photo diode is also decreased. As a result, the monitoring current is reduced as well. Thus, the automatic power control circuit 10 can duly adjust the current supplied to the laser diode according to the change of the monitoring current such that the output power of the laser diode may remain unchanged.
Due to the individual difference of the laser diode, the photo diode, and the packaging, each of the produced laser diode modules has different monitoring current. Therefore, the application terminal has to employ a variable resistance for producing a fixed monitoring voltage. However, the cost of the variable resistance is too high. When a fixed resistance is employed, the laser diode module has to be divided into many groups according to the created values of the monitoring current for obtaining a stable power output.